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Intubation methods for obese patients requiring general anaesthesia

Patients requiring general anaesthesia need assistance with breathing during the operation. To provide this, the anaesthetist may insert a tube through the mouth or nose and down the trachea (windpipe) into the lungs. This is known as tracheal intubation, and usually the intubator uses a metal instrument called a laryngoscope to position the patient so s/he can see the vocal cords directly (direct laryngoscopy). This can be a difficult procedure in obese men and women for various reasons, including fatty tissue in the neck and throat. Guidelines suggest the use of flexible intubation scopes (FISs) for tracheal intubation in obese people. These scopes allow the intubator to see the airway via a camera, but no reviews have examined the use of an FIS in this situation. Intubation with an FIS is considered an advanced method, requiring training and experience; therefore it may be underused in clinical practice. We aimed to compare the safety and effectiveness of an FIS used for tracheal intubation in obese patients with direct laryngoscopy and other intubation methods that give the intubator an indirect view of the larynx. These other methods include videolaryngoscopes (VLSs)—metal laryngoscopes that contain a camera. We found three small studies, with a total of 131 patients, that compared an FIS with a VLS. The results for all patient safety outcomes were inconclusive, and no differences were noted between intubation with a flexible scope and intubation with a videolaryngoscope. We are unable to make any recommendations for practice based on this review. More research is needed to identify the technique for intubating obese people that would offer the best success rate with the fewest complications.

Authors' conclusions:

The evidence base is sparse, and the existing literature does not address the clinical questions of patient safety posed by this review. We are therefore unable to draw any conclusions on safety or effectiveness. More primary research is needed to investigate optimal intubation techniques in obese patients, and new studies should be powered to detect differences in complications and in success rates rather than process measures such as speed, which are of limited clinical importance.

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Background:

The prevalence of obesity (body mass index (BMI) > 30 kg/m2) is increasing in both developed and developing countries, leading to a rise in the numbers of obese patients requiring general anaesthesia. Obese patients are at increased risk of anaesthetic complications, and tracheal intubation can be more difficult. Flexible intubation scopes (FISs) are recommended as an alternative method of intubation in these patients. Intubation with an FIS is considered an advanced method, requiring training and experience; therefore it may be underused in clinical practice. Patient outcomes following intubation with these scopes compared with other devices have not been systematically reviewed.

Objectives:

We wished to compare the safety and effectiveness of a flexible intubation scope (FIS) used for tracheal intubation in obese patients (BMI > 30 kg/m2) with other methods of intubation, including conventional direct laryngoscopy, non-standard laryngoscopy and the use of intubating supraglottic airway devices. We aimed to compare the frequency of complications, as well as process indicators, such as time taken for intubation and the proportion of first attempts that were successful, between groups using the different methods of intubation.

Search strategy:

We searched the Cochrane Central Register of Controlled Trials (CENTRAL), MEDLINE, EMBASE and two trial registers on 18 January 2013, and performed reference checking and citation searching and contacted study authors to identify additional studies.

Selection criteria:

We included randomized controlled trials (RCTs) of participants aged 16 years and older with a BMI > 30 kg/m2 that had compared the use of an FIS for tracheal intubationwith any one of three comparison groups: direct laryngoscopy; non-standard laryngoscopy (including indirect laryngoscopy using a videolaryngoscope (VLS) or a rigid or semi-rigid stylet); or intubation of supraglottic airway devices (SADs).

Data collection and analysis:

We used standard methodological approaches expected by The Cochrane Collaboration, including independent review of titles, data extraction and risk of bias assessment by two investigators.

Main results:

Three eligible studies were identified, all comparing the use of an FIS with a VLS. All studies were small, with only 131 participants in total across all trials. It was impossible for the intubators to be unaware of the device used, so all studies were at high risk of performance and detection bias for outcomes related to intubation. Because of substantial differences in design between the studies, we did not combine their results in meta-analyses. The results for all outcomes were inconclusive, with no differences noted between FIS and VLS. Two studies with experienced intubators reported first attempt success rates greater than 70% in both groups and less than 5% of participants requiring a change of intubation device. No evidence was found of any difference in difficulty or time taken between FIS and VLS intubation. No serious complications or airwaytrauma was reported, so we were unable to address these outcomes. Bleeding was uncommon, occurring in less than 5% of participants, and we found no evidence that it was more likely in the FIS group. One small study with a novice intubator reported no successful intubations using an FIS and compared with the use of an intubating SAD and stylet, as well as with a VLS. With only five participants in each group, no conclusions can be drawn from these additional comparisons.